iTunes and External Drive Issue

Hello apple community,

I have always kept my itunes library (media) on an external drive... I recently bought an old macbook (running El Capitan) and wanted to mirror my mac mini (running High Sierra) itunes setup onto that. I know, I could just share itunes libraries over wifi, but I want to use the DJ software Serato and that only syncs with the itunes of the machine it's installed on...

So, I bought a new external drive. Used Superduper! to clone my external drive containing nothing but the itunes media (named: Music) to the new one (named: MusicCopy). I also copied the itunes folder containing the .itl file from the Mac to the new external drive.

Now, on the new laptop, I deleted the old itunes folder, replaced it with the copied one. Then deleted that from the new external drive (MusicCopy). I opened itunes and all my playlists were there, but no media. I went into preferences and changed the media folder to Volumes/MusicCopy hit OK, but nothing... All the playlists are there but inside it just says there are 'No Items'...

Where have I gone wrong? Please help...

I just want to mirror the setup I have on my mac mini with my new macbook -All media on the external (MusicCopy), but I guess the itunes database files etc. on the macbook itself...

Thanks...